It is well known that some polymers will crosslink if subjected to high energy, ionizing radiation and that the physical and chemical properties of these polymers may be significantly improved by such a process. However, applications of this process have been limited by the relatively large radiation dosage required to significantly crosslink the polymer matrix.
More recently, it was learned that by the addition of certain monomers having multiple points of ethylenic unsaturation to the polymer prior to irradiation, the required radiation dosage could be reduced by as much as 60 to 70%. Apparently, each point of unsaturation reacts and forms a chemical bond with the polymer matrix, and the monomer thereby serves as a crosslinking agent similar to sulfur in conventionally vulcanized rubbers; such monomers are appropriately termed "crosslinking monomers". This development made the radiation crosslinking process economically feasible and sparked a great deal of interest in a variety of potential applications for radiation cured polymer materials.
In applying this technique to acrylonitrilebutadiene (hereinafter "NBR") elastomeric compositions, it was soon evident that trimethylolpropanetrimethacrylate (hereinafter "TMPT") was the most effective crosslinking monomer. However, in the development of articles made from a radiation cured NBR elastomer, it was discovered that the ultimate elongation of the material was severely reduced if TMPT were used to accelerate the crosslinking process. This loss of elongation rendered the product unsuitable for many applications.